I have a well stocked 75g and recently added about 10 pygmy corys and have already lost a few, so i want to ensure i am not doing anything wrong. One or two may have been hurt during transport from LFS (caught in a fold of the bag) but the third one that died was fine for a few weeks. The others are all fine and active but i just want to make sure i am properly caring for them. I monitor my water parameters weekly (no issues). Still change water 2-3x/month and have never lost any other fish in more than a year since i re-started in the hobby. Tankmates include a few species of tetra, a few 3 spot female gouramis, and some peaceful small chiclids. None of them bother the corys. What i am wondering is whether my substrate flourite black (not sand) could be an issue (i had read in this forum that it was ok for them) or maybe they are not getting enough food (i mostly use flakes but vary it up a bit. Open to any ideas thanks!!!